[dajiaohuang]

Problem

[[columns]] header accepts arbitrary strings, but --json interpolates the header without JSON escaping. For example, a supported configuration containing:

[[columns]]
kind = "Pid"
header = 'Process "ID"'

produces a field like "Process "ID"": 201, so a JSON consumer cannot parse the output. Backslashes and control characters in custom headers have the same problem.

Change

JSON-encode the header with serde_json, retaining existing numeric/string value handling and the default key names. Declare the dependency directly so this also works with --no-default-features (the default Docker dependency already brings it into Cargo.lock). Add a platform-independent regression for ordinary headers, quotes, backslashes, newlines and tabs.

Validation

• Regression passes with default features and --no-default-features on Windows x86_64, Rust 1.98.1.
• A local synthetic-record harness exercised production columns and View::filter/adjust/display: the quoted-header JSON failed on base and passes with this change. No host process table was collected.
• Existing JSON object and regex tests pass in both feature configurations; cargo fmt -- --check passes.
• cargo clippy -- -D warnings fails on five existing unnecessary casts in src/columns/priority.rs:140–144; the unchanged base has identical diagnostics, with and without default features.
• Full process-collecting tests and interactive/live-OS acceptance were not run in this shared environment. Synthetic rendering tests do not establish OS collector acceptance.